This invention relates generally to X-ray inspection systems and more particularly to industrial X-ray systems which use digital detectors.
Recent advances in medical X-ray technology have provided a new generation of digital X-ray detectors, such as charge-coupled devices and amorphous silicon arrays, which have many advantages over traditional detection equipment and methods. These digital X-ray detectors are often adapted for use in industrial X-ray systems, which employ much greater voltage and energy than are typically used in medicine. One problem faced in using medical X-ray detectors to inspect industrial parts is that at these higher energies and corresponding voltages, the approaches used in medicine to control the X-ray source are not available on commercially available industrial X-ray sources.
X-ray tubes produce X-rays by accelerating electrons into a dense (generally tungsten) target. These tubes use electromagnetic or electrostatic steering methods to control the location of the electron beam impact on the target, and these methods consequently control the location and size of the X-ray focal spot. Several of the types of electronic detectors used in medical and industrial imaging either require that the X-ray flux be eliminated while the detector""s signal is read and transferred to the downstream computing systems, or exhibit improvement in image quality if this is done. In lower voltage systems, i.e. less than about 225 KV, the X-ray tube""s electron beam is controlled, starting and stopping the electron flow, effectively switching the tube""s X-ray flux on and off in synchronization with the detector sampling period. The X-ray flux is created for a period of time during which X-ray photons penetrate the inspected object and then continue to the detector where they are counted or converted into measurable or accumulated charge. The X-ray flux is then turned off while the detector is read. As X-ray energies increase, it becomes increasingly difficult to accomplish this switching, and the commercial requirements for such industrial tubes decline in number. Methods such as simple tube grids that stop the tube""s electron flow and other methods employed to pulse the electron beam are not available at higher tube voltages. When the X-ray flux can not be pulsed in this manner, image quality in electronic detector systems is degraded. This makes it difficult to employ these detector technologies in many industrial applications requiring higher energies. Furthermore, it is desirable to minimize the X-ray dose delivery to the detector to extend its lifetime. This is a constraint for certain equipment and for certain applications, and is becoming a larger issue with amorphous silicon detectors.
Accordingly, there is a need for a method of pulsing the X-ray flux in an industrial X-ray inspection system.
The above-mentioned need is met by the present invention, which provides an X-ray inspection system comprising an X-ray source which includes an electron gun and beam steering means for alternately directing the electron beam from the gun in a first direction wherein the beam strikes the anode to produce a beam of X-rays which exits the X-ray source, and in a second direction wherein no significant X-ray flux exits the X-ray source. An X-ray detector and means for reading the detector are also provided. The beam steering means and the detector reading means are coordinated so that the detector output is read during a period when no significant X-ray flux exits the source. The present invention also provides a method for operating the X-ray inspection system.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.